Mapping Antarctic Grounding Lines from ICESat-2 Laser Altimetry

The grounding line is the point where the grounded ice sheet detaches from the bed and begins to float. Knowledge of its position and dynamics are critical in mass budget assessments, ice sheet instability monitoring and ice sheet numerical modelling. The grounding line is typically mapped from the landward limit of tidal flexural using different satellite techniques, such as differential synthetic aperture radar interferometry (DInSAR) and ICESat-1 laser altimetry repeat track analysis. However, these methods have, to date, been limited by either spatial or temporal coverage. Launched on 15 September 2018, ICESat-2 satellite offers the potential to address both spatial and temporal coverage issues. Its six-beam pattern as well as the small footprint (~17 m in diameter) and high pulse repetition frequency (10 KHz) of laser altimeter instrument, can achieve a higher accuracy and an order of magnitude denser spatial coverage than ICESat-1. Here we present the results of mapping the grounding line position in Antarctica by detecting the landward limit of tidal flexure from a combination of ICESat-2 repeat track data with a crossover analysis of ascending and descending tracks. Grounding line positions mapped from this method are compared with previous estimates from DInSAR, ICESat-1 altimetry and the break-in-slope mapped from optical imagery. The results show an overall good agreement and highlight the improvements with the new satellite to provide high accuracy and density observations of grounding line in both space and time.